A problem associated with storing edible aquatic animals, such as fish and sea products, in a frozen state is the decomposition of trimethylamine-oxide (TMAO) and the formation of volatile trimethylamine (TMA), which is the source of the unpleasant “fish” odor of the product. The main reasons for this odor include destruction of cellular and intracellular membranes during freezing and thawing of the product and subsequent release of enzymes involved in the formation of TMA from TMAO, as well as decomposition of TMAO with subsequent formation of TMA as a result of heating the product.
One known method of preventing the destruction of cellular and intracellular membranes while storing biological materials is to add cryoprotectors, such as different saccharides (monosaccharides, disaccharides, oligosaccharides, polysaccharides, etc.) to the material prior to freezing. For instance, in the method described in U.S. Pat. No. 5,910,331 “Method of freeze-preserving vegetables”, vegetables are soaked in a solution that contains polysaccharides and disaccharides. After soaking, the product is quickly frozen. It is believed disaccharides, penetrating the cells of the product during soaking, provide a cryoprotective (freeze-preservation) action during the process of freezing/thawing. Similarly, in the method described in JP 6319501 “Novel frozen food”, 0.5-10% (w/w) of disaccharide (trehalose) is added to the product and then the product is frozen. In this case, it is considered the product is protected from damage caused by the freezing/thawing process. However, each of the aforementioned methods have significant disadvantages because the product must be soaked in the saccharides for a long period of time so that there is sufficient penetration of the cells. Since the product is not a live organism when it is treated with the cryoprotectant, autolysis and bacterial putrefaction processes occur, destroying some cells, which, in turn, will adversely affect product quality.
In the method described in U.S. Pat. No. 6,576,281 “Method for inhibiting trimethylamine formation”, a fish is first killed and an edible portion of the raw fish food product (for example, fish filets or sea products) is soaked or boiled in a trehalose solution and then cooked. While this method inhibits TMA forming from TMAO in the uncooked fish products, it is used to treat dead animals, which likely creates a higher concentration of trehalose in the meat closer to the product surface, which may alter the taste of the product such that it becomes noticeably and unnaturally sweeter.
The method described in JP 2004129622 “Feed for fish culture”, discloses adding 0.1-0.8% w/w of trehalose to fish food. The purpose of the food additive is to accelerate growth and improve the feeding efficiency and survival of fishes and crustaceans. The fish are not intended for human consumption and are therefore not processed for that purpose.